Process of treating hydrocarbon oils



Nov. 7, 1939. J. w. GRAY ErAL PROCESS OF TREATING HYDRCARBON 01?;

Filed Aug. 19, 1937 Patented Nov. 7, 1939 UNITED STATES PATENT OFFICEPROCESS F TREATING HYDROC'ARBON ILS poration of Delaware ApplicationAugust 19,

11 Claims.

This invention relates to an improvement in the art of crackinghydrocarbons to produce lowboiling hydrocarbons from high-boilinghydrocarbons.

In the treatment of hydrocarbons to produce cracking thereof, it isknown to mix hot heavy oil such as topped or reduced crude oilcontaining heavy constituents with a hot, partially cracked clean oiland then to further crack this mixture.

These processes sometimes result in coking in the coils because thereseems to be a limit to the temperature to which the mixed hot heavy oilsand cracked clean oils can be further heated without coking. Theobjectionable coking seems to result because the hot heavy oils andextremely hot clean oils do not apparently mix instantly and uniformlyapparently causing overheating of some of the heavy oils by contact withthe high-temperature clean oils to cause the formation of coke.

We have overcome the above-mentioned objection by mixing all of the hotheavy oil charge with only a part of the highly heated clean oil or gasoil coming for example from the rst portion of a cracking zone in theradiant section of a furnace and passing this mixture for examplethrough either the latter portion of the cracking zone in the convectionsection of the furnace or through an insulated section situated outsideof the furnace, with the remainder or part of the remainder of thehighly heated clean oil or recycle gas oil coming from the rst portionof the cracking zone being injected at a subsequent point or points inthe combined stream. If desired, part of the highly heated clean oilfrom the radiant section of the furnace may be passed through the latterportion of the cracking Zone in the convection section of the furnaceand the remainder passed through an insulated section situated outsideof the furnace. In this way the temperature of the combined stream ismaintained or progressively raised, and the cracking rate iscorrespondingly increased thus resulting in efiicient viscosity-breakingof the heavy oil. The stream or charge of highly heated clean oil orrecycle gas oil coming from the first portion of the cracking zone maybe subdivided as much as desired and injected into the latter portion ofthe cracking zone at a plurality of selected points. Our method isespecially advantageous in cases where the temperature of the crackedclean oil or recycle gas oil is exceptionally high, such as when theclean oil is subjected to socalled vapor phase cracking.

Other advantages will be apparent` from the 1937, Serial N0. 159,866

detailed description of our invention hereinafter contained taken inconnection with the drawing which shows a diagrammatic iiow sheet ofapparatus adapted for practicing our invention.

Referring now to the drawing, the reference 5 character Il) designates aheater or furnace having a continuous heating coil I2 Where theoil to beconverted is maintained under superatmospheric pressure andhigh-temperature conditions for a desired length of time to obtain thedesired 10 cracking or conversion. The rst portion I3 of the crackingcoil extends through the radiant section I4 of the furnace and thelatter portion I5 of the cracking coil extends through the convectionsection I6. The oil to be cracked is prei- 15 erably a clean oil, suchas gas-oil condensate or heavy naphtha, and this clean oil is passedthrough line 20 by means of pump 22 through the radiant coil section I3of the cracking coil I2 and is maintained under high-temperature and 20high-pressure conditions during its passage therethrough to effectconversion into lower boiling products. The stream of high-temperaturecracked products leaves the first portion I3 of the cracking coil I2through line 24 and is sub- 2l'- divided into two portions for passageof a separate portion through each of lines 2B and 23. A heavy oilcontaining unvaporized liquid constituents of a reduced crude oil andheavy reux condensate, obtained as later described, is passed 30 throughline 3U by means of pump 32 and is injected into or admixed with thatportion of the cracked products passing through the line 26. In this waythe heat of a part of cracked products is utilized to materiallyincrease the tem- 35 perature of the heavy oil, preferably to a crackingtemperature.

The combined stream at cracking temperature is passed through the latterportion I5 of the cracking coil I 2 extending through the convec- 40tion section I 6 of the furnace II) and is therein subjected toadditional heating by the furnace gases. The other portion of thestream'of the high-temperature cracked products passing through line 28may be passed through line` 34 45 and admixed With the combined streamunder- .f going cracking at an intermediate point in the coil section I5extending through the convection section IB of the furnace I ll, or onlya part of the stream may be so injected and the rest, passing 50 throughline 36, may be injected into the stream of cracked products leaving thecoil section l5 through line 4D. v When a part of the high-temperaturestream is injected into the combined stream, as for example through line34, the tem- 55 perature of the combined stream at this point is raisedand the cracking rate increased. If desired, the combined stream may bepassed through a reaction chamber wherein further cracking may beeffected..

The stream of cracked. products after the deaired conversion thereof hasbeen completed is passed through line 09 preferably having a reducingvalve 42 into the evaporator or separating Zone 44 of the combinedevaporator and fractionating tower 46 having a fractionating section 48.Suitable quenching stock such as gas-oil or lighter may be introducedthrough line 4,9 into the stream passing through line 453 to cool thecracked products suddenly and prevent overcracking thereof. Theevaporator section 44 and the fractionating section 48 of the combinedevaporator and fractionating tower 15G are separated by a trap-out trayhaving a hood 52. In the evaporator the pressure is preferably lowerthan in the cracking Zone and the stream of cracked products passinginto the evaporator 4.4 is separated into hot vapors and a crackedresidue. The hot vapors pass upwardly into the fractionating section 48.

The cracked residue is withdrawn from the bottom of the evaporator 44through line 55 having a pressure reducing valve 58 and passed into theflash zone E8 of the combined fractionating and flash tower 62 having afractionating section 66. The flash zone 80 and fractionating section 66of the combined fractionating and ash tower 62 are separated by atrap-out tray 68 provided with a hood 10. The flash Zone 60 is underless pressure than the evaporator 44 so that a flash distillation orvaporization is obtained and a further separation into hot vapors and acracked residue takes place in the flash zone 60. The cracked residue issuitable for use as fuel oil and may be withdrawn through line 'I2 andfurther treated if desired. The hot vapors released in the ash zone E0pass upwardly into the fractionating section 66 of the combinedfractionating and flash tower 52 where r they come in contact withdownwardly flowing reduced crude oil, or other fresh heavy oil,preferably preheated. The reduced crude oil charge or heavy oil ispassed through line 'l5 by means of pump 18 into the upper portion offractionating section 68 where it cornes in contact with the hot vaporsreleased from the flash Zone 60 and some of the crude oil is vaporizedand some of the vapors in the fractionating section 6E are condensed toform reflux condensate. The vapors may be withdrawn through line i9 andmay be separately treated as desired, but are preferably forced into asecondary fractionating zone, later to be described, for furthertreatment.

The heavy reflux condensate and unvaporized reduced crude oil arecollected on trap-out tray 58 at the bottom of the fractionating sectionG6. The reflux condensate and unvaporzed reduced crude oil are passedthrough line 80 by means of pump 82 into the upper portion offractionating section 48 of the combined evaporator and fractionatingtower 45S where they come in contact with hot vapors released from theevaporator 44. Some of the liquid constituents are vaporized and thecombined vapors are fractionated in the fractionating section 48 of thecombined evaporator and fractionating tower 45 wherein some of thevapors are condensed to form heavy reflux condensate. The heavy refluxcondensate and unvaporized reduced crude oil are collected in trap-outtray 50 at the bottom of the fractionating section 48 and form the heavyoil charge which is passed through line 30 into the coil section l5 orlatter portions of the cracking coil |2 extending through the convectionsection I6 of the furnace I0.

The vapors leaving the top of the combined evaporator and fractionatingtower 46 are passed through line 84 into the bottom portion of thesecondary fractionating Zone 86 which, prefer ably, is of bubble towerconstruction. As the vapors pass upwardly in the secondary fractionatingzone 8S they are fractionated into lighter and heavier constituents, thelighter constituents passing over as vapors and the heavier constituentsbeing condensed and collected at the bottom of the secondaryfractionating zone 86 as condensate oil. This condensate oil is agas-oil which contains insucently cracked products and is the clean oilwhich is passed through line 20 and coil section I3 extending throughthe radiant section I4 of the furnace l0 to be converted.

The vapors of the desired end point leaving the top of the secondaryfractionating zone 86 are passed through line 88, cooled and condensedby passing through condenser 90 and the liquid is collected in asuitable receiver or drum 92. The receiver or drum 82 has a valved gasoutlet 84 and a valved liquid outlet 9E. The liquid which is collectedon the bottom of receiver or ,f

drum 92 comprises a motor fuel product such as gasoline which may befurther treated as desired. The vapors leaving the top of the combinedfractionating and flash tower 62 are passed through line 1S as abovementioned and may be separatei ly treated as desired, but they arepreferably forced into line 84 in any suitable manner and passed to thesecondary fractionating Zone 86 along with the vapors passing throughline 84.

Some of the liquid collecting on the bottom of the receiver or drum 92is preferably passed through line |00 by means of pump |52 into theupper portion of the secondary fractionating zone 88 to act as refluxliquid. If desired, a cooling coil |04 may be mounted in the upper partof the secondary fractionating zone 86 to provide additional cooling forthe upper portion of the secondary fractionating Zone 86.

If desired, a portion of the heavy oil leaving the bottom of thefractionating section 48 of the combined evaporator and fractionatingtower 4G may be passed through line |06 and then through a heating coil|08 in order to preheat the heavy oil or subject it to a relatively mildviscositybreaking treatment. The heated heavy oil leaving the heatingcoil |08 may then be4 passed through line H0 and into the line 30'leading to the latter portions of the coil section I5 as described.

Instead of passing all the reduced crude oil into the fractionatingsection 5t of the combined fractionating and flash tower 62, a part ofthe reduced crude oil may be passed through lines H6 and ||8 and thenthrough the heating coil |08 in order to preheat it or subject it to amild viscosity-breaking treatment. The heated oil leaving the heatingcoil |88 is then passed through line |I0 for admixture with heavy oilwithdrawn through line 30 for passage through the latter portion of thecoil section I5 as described.

We have found that by injecting the heavy oil passing through line 30into a part of the highly heated stream of cracked products coming fromthe first portion or section of the cracking 'Sie zone l2, we avoidobjectionable coking. obtained when all of the heavy oil and thehigh-temperature clean oil are mixed together. The clean oil and theheavy oil apparently do not'mix instantly and uniformly when all of thecracked clean oil is mixed, and some of the heavy oil may becomeoverheated by contact with the hightemperature clean oil and cause theformation of coke. By dividing the high-temperature clean oil into twoor more streams and injecting the heavy oil into one of the streams andthen cracking such mixture we overcome the objections heretofore noted.

When the temperature necessary to crack the clean oil passing throughthe rst portion of the cracking zone l2 is extremely high, it will bedesirable to use a plurality of injection points into the combinedstream passing through the latter portion or section l5 of the crackingZone I2.

The vapors from the top of the combined fractionating and iiash tower S2containing both gasoline and gas-oil constituents may be completelycondensed and mixed with the condensate being passed through thecracking zone i2 to effect cracking of the gas-oil and reforming of thenaphtha contained therein.

An example of a typical operation will now be given, but we are not tobe restricted thereto as various changes and modications may be made. Areduced crude oil stock or other relatively heavy charging stockpreferably preheated in any suitable manner is introduced into thefractionating section 65 of the combined fractionating and iiash tower52, maintained at apres-- sure of between atmospheric and 50 pounds' persquare inch, where it contacts hot vapors passing upwardly from the ashzone 50 and thus vaporizes some of the light constituents from thereduced crude oil or heavy oil charge. At the same time some of theheavier constituents of the hot vapors are condensed to form heavyreflux condensate. The heavy reflux condensate and unvaporized liquidare collected at the bottom of the fractionating section as, forexample, in trap-out tray t8 and are then passed through line St by pumpS2 to the fractionating section d8 of the combined evaporator andfractionating tower maintained at a pressure of between about 50 and 100pounds per square inch, where some of the liquid is vaporized andfractionated by contacting the hot vapors from the evaporator orseparating zone le of the combined evaporator and fractionating towerfit. Some of the heavy constituents of the vapors condense to formreflux condensate.

The unvaporized heavy constituents and reiiuX condensate are collectedat the bottom of the fractionating section "i8 in trap-out tray 5t. Thevapors leave the top of the combined evaporator and fractionating towerd3 at a temperature of about 650750 F. and pass through line 8f3 intothe bottom of the secondary fractionating tower 86 to be fractionatedtherein. The vapors leaving the secondary fractionating zone 0G throughline 88 are at a temperature of about SOW-400 F. and are condensed andcollected in receiver 02 as low-boiling hydrocarbons suitable for motorfuel, such as gasoline, after further usual treatment.

The gas-oil condensate from the bottom of the secondary fractionatingzone 86 containing insufliciently cracked products comprises the cleanoil or recycle gas-oil which is passed 'through line 20 and into the rstportion i3 of the cracking zone l2 extending through the radiant sectionI4', of the furnace l0. This clean oil enters the cracking zone at atemperature of about 550 to 700 F. and leaves the cracking zone at atemperature of about 925 to i100" F. and during its iiow therethrough issubjected to cracking; This highly heated stream of cracked productspasses through line 2li and is then subdivided into two streams. Onestream passing through line 26 is combined with the heavy oil passingthrough line 30 from the trap-out tray 50 in the combined evaporator andfractionating tower d6, the heavy oil being at a temperature of about600 to 900 F. After the injection of the heavy oil into the stream ofthe high-temperature cracked clean oil passing through line 26, thecombined stream is at a temperature of about 850 to 925 F., and thiscombined stream is then passed through the latter portion l5 of thecracking zone l 2 extending through the convection section i6 whereinfurther cracking of the clean oil and viscositybreaking of the heavy oiltakes place. The combined stream leaves the cracking zone at about 850to 950 In the cracking zone the pressure is maintained at about 300 to1000 pounds per square inch.

The other portion of high-temperature cracked clean oil passing throughline 28 may be injected at a subsequent point through line 34, for eX-ample, into the combined stream passing through the latter portion l5 ofthe crackingvcoil i2 extending 'through the convection section lli ofthe furnace i0 to raise the temperature of the combined stream andincrease the cracking rate; or this portion may be passed through line36 to by-pass the latter portion it of the cracln'ng zone i2 and beinjected into the stream of cracked products leaving the latter portionof the cracking zone through line t0.

The stream of cracked products leaving the latter portion of thecracking zone l2 through line Iltis passed into the evaporator orseparating zone Sii. The separating zone dit is maintained at a pressureof about 50 to 350 pounds per square inch and a separation of thecracked products into hot vapors and a cracked residue occurs. The hotvapors are fractionated in the fractionating section S of the combinedevaporator and fractionating tower l5 and this fractionation is assistedby contact with hot liquid introduced into the tower it through line 80from the combined fractionating and flash tower t2. lighter constituentsof the liquid are vaporized and some of the heavier vapors are condensedto form reflux condensate.

The vapors leave the top of the combined evaporator and fractionatingtower it at a temperature of about 650 to '750 F. and pass through lineSfiinto the bottom portion of the secondary fractionating zone Thevapors passing upwardly in the secondary fractionating zone' are thereinfractionated to condense insuiciently cracked products as refiuxcondensate and the remaining vapors of lower-boiling hydrocarbons, thatis, the desired gasoline, are condensed and collected in receiver 92.'rIhe condensate collected in the bottom of secondary fractionating zone86 forms the clean recycle gas oil which is recycled through thecracking zone i2 through line 20.

In the fractionating section d8 some of the The crackedl residue fromthe separating Zone M in the bottom of the combined evaporator andfractionating zone d is passed through line 56 having reducing valve 58and into the ash zone 60 in the bottom of the combined fractionating andash tower 62 maintained at a lower pressure than separating Zone 44. Aflash distillation takes place in flash zone- 44 and the hot vapors andcracked residue are Separated. The hot vapors from the ash zone 60 passupwardly and contact the hot reduced crude oil charge or other heavy oilintroduced into the fraotionating section 66 ofthe combinedfractionating and ash tower 62. Vaporization of some of the lighterconstituents of the crude oil and condensation of some of the heavierconstituents from the hot vapors are effected in the fractionatingsection 66. The vapors leaving the top of the combined fractionating andflash tower 62 through line 19 may be passed to the fractionating zone8G with insumciently cracked products therefrom being added to thereflux condensate therein for passage through the cracking Zone I2 forcracking. The cracked residue from the bottoml of flash zone El] may bedrawn off through line 12 and used as iuel oil.

It is within the contemplation of our invention to omit the combinedfractionating and ash tower 62, in which event the reduced crude oilcharge or other relatively heavy oil charge would be introduced into thefractionating section 48 of the combined evaporator and fractionatingtower 46; and the unvaporized liquid or cracked residue separated fromthe stream of cracked products introduced into the evaporator orseparating zone 44 would be withdrawn from the bottom of the evaporator44. The unvaporized heavy oil and heavy reflux condensate collecting ontrap-out tray 5i) would be passed through line as hereinbeforedescribed.

While we have described a particular embodiment of our invention, it isto be expressly understood that our invention is not restricted thereto,and various modications and adaptations thereof may be made withoutdeparting from the spirit of the invention.

We claim:

1. A process for treating high-boiling hydrocarbons to producelow-boiling hydrocarbons, which comprises contacting vapors in a primaryfractionating zone With a relatively heavy oil and collectingunvaporized heavy oil therein, thereafter subjecting vapors from theprimary fractionating Zone to further fractionation in a secondaryfractionating Zone to separate relatively high boiling oil therefrom asreiiux condensate, passing reux condensate thus obtained as a streamthrough the first portion of a cracking zone maintained underhigh-temperature and high-pressure conditions to produce conversion ofsuch reux condensate into lower boiling products, injecting unvaporizedheavy oil from said primary fractionating zone into a portion of thestream of high-temperature cracked products leaving the rst portio-n ofthe cracking Zone, passing such combined stream through the latterportion of the cracking zone maintained at cracking temperature,injecting another portion of the stream of high-temperature crackedproducts into the latter portion of the cracking zone at a pointsubsequent to the injection of such heavy oil to raise the temperaturethereof and effect further cracking of the heavy oil, passing theresulting stream of cracked products leaving the latter portion of thecracking zone to a separating zone wherein vapors and cracked residueare separated, and passing such vapors into the primary fractionatingzone.

2. A process for treating high-boiling hydrocarbons to produce`low-boiling hydrocarbons,

which comprises contacting vapo-rs in a primary fractionating Zone witha relatively heavy oil and collecting unvaporized heavy oil therein,thereafter subjecting vapors from the primary fractionating zone tofurther fractionation in a secondary fractionating zone to separaterelatively high-boiling oil therefrom as reflux condensate, passingreflux condensate thus obtained through the rst portion of a crackingzone maintained under high-temperature and highpressure conditions toproduce conversion of such reflux condensate into lower-boilingproducts, then subdividing such stream of cracked products into twoportions and injecting the unvaporized heavy oil from said primaryfractionating zone into one portion of the stream of cracked productsand passing such combined stream through the latter portion of thecracking zone maintained at cracking temperature, and injecting theother portion of the stream of cracked products into the combined streamleaving the latter portion of the cracking zone, and passing this newlyformed stream of cracked products to a separating zone wherein vaporsand. a cracked residue are separated, and passing the vapors into theprimary ractionating Zone.

3. A process for treating high-boiling hydrocarbons to producelow-boiling hydrocarbons, which comprises contacting a reduced crude oilwith hot vapors to vapo-rize some of the crude oil and condense some ofthe heavy constituents of the vapors as relatively heavy refluxcondensate, passing remaining vapors to a fractionating Zone to thereinseparate high-boiling oil as reux condensate, collecting the unvaporizedreduced crude constituents and relatively heavy reux condensate, passingreflux condensate thus obtained as a stream through the rst portion of acracking zone maintained under relatively high-temperature andhigh-pressure conditions to produce conversion thereof intolower-boiling products, injecting the unvaporized reduced crudeconstituents and relatively heavy condensate into one portion of thestream of high-temperature cracked products from the rst portion of thecracking zone, passing sucht combined stream through the latter portionof the cracking zone maintained at a cracking temperature, injectinganother portion of the stream of high-temperature cracked products fromthe first portion of the cracking zone into the latter portion o-f thecracking zone at a point subsequent to the injection of the unvaporizedreduced crude constituents and relatively heavy condensate to raise thetemperature and effect further cracking of the introduced reduced crudeconstituents and relatively heavy condensate, passing the resultingstream of cracked products to a separating zone wherein hot vapors andcracked residue are separated, and using such hot vapors to contact thehot reduced crude oil to be treated.

4. A process for converting higher-boiling hydrocarbons intolower-boiling hydrocarbons, which comprises passing relatively heavy oilto a fractionating zone to contact hot vapors therein and vaporize someof the lighter constituents of the heavy oil and to condense some of thehot vapors therein to form heavy reflux condensate, passing theremaining vapors to a secondary fractionating zone to produce lightproducts and a gas-oil condensate, passing such gas-oil condensate intothe first portion of a cracking zone maintained under high-temperatureand highpressure conditions to produce conversion of the gas-oilcondensate into cracked products, injecting the heavy reflux condensateand unvaporized heavy oil from the irst-mentioned iractionating zoneinto one portion of the stream of high-temperature cracked productspassing through the latter portion of the cracking zone, passing suchcomb-ined stream through the latter portion of the cracking zone,injecting another portion of the stream of high-temperature crackedproducts into the latter portion of the cracking Zone at a pointsubsequent to the injection ofthe heavy reflux condensate andunvaporized heavy oil, injecting the rest of the stream ofhigh-temperature cracked products into the stream of converted productsleaving the latter portion of the cracking Zone, passing such newlyformed stream of cracked products to a separating zone wherein hotvapors and cracked residue are separated, and passing such hot vaporsinto the first-mentioned fractionating zone for contact with the heavyoil introduced thereinto.

5. In a process for converting higher-boiling hydrocarbons intolower-boiling hydrocarbons wherein a stream of cracked products from acracking zone is separated into vapors and cracked residue and thevapors are fractionated in primary and secondary fractionating Zones andcondensate oil containing insufficiently cracked products is collectedin the secondary fractionating zone, the steps comprisingy passing thecondensate oil through a portion of the cracking zone maintained underhigh-temperature and high-pressure conditions to convert the condensateo-il into lower-boiling hydrocarbons, injecting a preheated heavy oilinto a portion of the stream of high-temperature cracked products andpassing such combined stream at cracking temperature through anotherportion of the cracking Zone, and then injecting another portion of thestream of high-temperature cracked products into the combined streampassing through the cracking zone, passing the cracked products from thecracking Zone to a separating zone to obtain the aforementioned vaporsand cracked residue.

6. A process of converting higher-boiling oils into lower-boiling oneswhich comprises, subjecting a relatively clean oil in a stream oirestricted cross-sectional area to elevated conditions of temperatureand pressure to eect conversion thereof into lower-boiling hydrocarbons,thereafter dividing said stream into at least two portions, admixing arelatively heavy hydrocarbon oil with one of said portions, passing saidmixture through a heating zone and subjecting the mixture therein toelevated conditions of temperature and pressure to effect conversion ofsaid heavy oil, and, thereafter admixing another portion of said dividedstream with said admixed stream to raise the temperature of the admixedstream.

7. A process of converting higher-boiling oils into lower-boiling oneswhich comprises, subjecting [a relatively clean oil in a stream ofrestricted cross-sectional area to elevated conditions of temperatureand pressure to eiect conversion thereorn into lower-boilinghydrocarbons, thereater dividing said stream into at least two portions,adlnixing a relatively heavy hydrocarbon oil with one of said portionsand heating said mixture to subject it to elevated conditions oftemperature and pressure to effect conversion of said heavy oil,combining said admixed stream with the other portion of said dividedstream and subjecting the resultant combined proding the primary sectionof thepassageway to I,.-

maintain the stream iiowing therein at cracking temperature, diverting aportion of the heated stream from the primary section of the passagewaywhile the remaining portion iiows to the intermediate section,introducing aI heavyfoil stock into sai-d remaining portion of thestream for passage through said intermediate section, heating saidintermediate section of the passageway and maintaining the resultantstream mixture at cracking temperature, uniting said diverted portion ofthe stream with the heated stream mixture for passage through thesubsequent section of the passageway, heating said subsequent sectionand maintaining the composite stream flowing therein at crackingtemperature.

9. A process for converting higher boiling hydrocarbons into lowerboiling hydrocarbons that comprises passing the hydrocarbons in acontinuous stream undergoing conversion successively through a primarysection, an intermediate section and a subsequent section of apassageway of restricted cross-sectional area, heating the primarysection of the passageway to maintain the stream flowing therein atcracking temperature, diverting a portion of the heated stream from theprimary section oi the passageway while the remaining portion flows tothe intermediate section, introducing a heavy oil stock into saidremaining portion of the stream for passage through said intermediatesection, heating said intermediate section of the passageway andmaintaining the resultant stream mixture at cracking temperature,uniting the diverted portion of the stream with the heated streammixture to thereby raise the temperature of the stream flowing in thesubsequent section of the passageway.

10. A process for converting higher boiling hydrocarbons into lowerboiling hydrocarbons that comprises passing the hydrocarbons in acontinuous stream undergoing conversion suc-u cessively through aprimary section, an intermediate section and a subsequent section of apassageway of restricted cross-sectional area, heating theprimarysection of the passageway to maintain the stream owing therein atcracking temperature, diverting a portion of the heated stream from theprimary section of the passageway while the remaining portion flows tothe intermediate section, passing av heavy oil stock through a separateheating zone wherein the oil is heated to a cracking temperature andsubjected to viscosity breaking, introducing resultant viscosity brokenproducts into said remaining portion of the stream for passage throughsaid intermediate section of said passageway, heating said intermediatesection of the passageway and maintaining the resultant stream mixtureat cracking temperature, uniting at least a part of said divertedportion of the stream with the heated stream mixture `for passagethrough the subsequent seotion of the passageway, heating saidsubsequent section and maintaining the composite stream owing therein atcracking temperature.

11. In a process for converting higher boiling hydrocarbons into lowerboiling hydrocarbons wherein the hydrocarbons are passed in a continuousstream undergoing conversion successively through a primary section, anintermediate section and a final section of a passageway of restrictedcross-sectional area thence into a separating Zone, the method thatcomprises heating the primary section of the passageway to maintain thestream flowing therein at cracking temperature, diverting a portion ofthe heated stream from the primary section of the passage- Way while theremaining portion flows to the intermediate section, introducing a heavyoil stock into said remaining portion of the stream for passage throughsaid intermediate section, heating said intermediate seation of thepassage- Way'and maintaining the resultant stream mixture at crackingtemperature, uniting a part of said diverted portion of the stream withthe heated stream mixture for passage through the nal section of thepassageway, heating said nal section and maintaining the' compositestream o-wing therein at cracking temperature, and combining anotherpart of said diverted portion of the stream with the composite productsowing from the final section of the passage- Way for passage to saidseparating zone.

JAMES W. GRAY. JESSE S. WALTON.

